1. Field of the Invention
The present invention relates to a structure of a semiconductor laser, in particular, a structure of semiconductor laser using a II-VI compound semiconductor, which oscillates in a blue-green region.
2. Description of the Related Art
A blue-green II-VI compound semiconductor laser has been reported in, for example, Appl. Phys. Lett. 62, 2462 (1993). This semiconductor laser includes: a Zn.sub.0.8 Cd.sub.0.2 Se single quantum-well active layer (thickness: 6.5 nm): a pair of ZnS.sub.0.06 Se.sub.0.94 optical confinement layers sandwiching the active layer; and a pair of Zn.sub.0.9 Mg.sub.0.1 S.sub.0.1 Se.sub.0.9 cladding layers sandwiching the pair of optical confinement layers and the active layer. One of the pair of ZnS.sub.0.06 Se.sub.0.94 optical confinement layers is doped with a p-type impurity, and the other is doped with an n-type impurity. It has been reported that this semiconductor laser oscillates at room temperature and emits a laser beam having a wavelength of 516 nm.
However, the above-mentioned semiconductor laser is disadvantageous in that a threshold current is relatively high. This is because an optical confinement factor with respect to the active layer is not sufficiently high.
The laser oscillation initiates when a mode gain becomes equal to a threshold loss of a laser resonator cavity. The threshold loss is inversely proportional to the optical confinement factor. Therefore, the larger the optical confinement factor is, the lower a current for driving the semiconductor laser can be. Since the optical confinement factor is relatively low, i.e., 1.7% in the above-mentioned semiconductor laser, a threshold current thereof is relatively high, i.e., 240 mA.